In the field of machine tools, effective ejection of the chips and machining fluid has been one of the important subjects for the research and development. For example, Japanese Unexamined Patent Publication (Kokai) No. 10-328968 describes a machine tool as a first prior art. This comprises a splashguard for enclosing a machining zone, a trough extending in the back-and-forth direction along the center of a bed, guides, provided on the bed at the left-and-right sides of the trough, for the back-and-forth motion of a table, the table being disposed over the trough, a single feed screw, provided at the center beneath the table, for feeding the table in the back-and-forth direction, and a cover for covering the guides and the feed screw wherein the chips and machining fluid falling into the trough are ejected from the machine.
Japanese Unexamined Patent Publication (Kokai) No. 2000-33530 describes a machine tool as a second prior art. This is an improvement of the invention of the first prior art, and has a difference in the configuration that, instead of the single feed screw disposed at the center beneath the table, a single feed screw is disposed at each of the left-and-right sides of the trough, i.e., two screws. This allows increase in the size of the opening of the trough so that the chips and fluid can easily fall into the trough.
On the other hand, although there is not described in the above two documents, some machine tools comprise spindle nozzles, disposed around the spindle, for directing the machining fluid to the machining zone between the cutting edge of a tool and a workpiece or shower nozzles for downwardly directing the machining fluid from the ceiling of a splashguard to wash away the chips on a workpiece, a workpiece mount, the top of a table and/or covers into the trough. In the trough, there is provided a mechanical chip conveyer which ejects the fallen chips and the machining fluid from the machine or a fluid chip conveyer which conveys the chips with the pressure of machining fluid directed in one way. A pump and a fluid circuit for supplying the machining fluid to a chip conveyer nozzle of the fluid chip conveyer is usually provided separately from the pump and the circuit for a process nozzle.
According to the first prior art, the screw for feeding the table and the cover for the feed screw is disposed at the center of the trough. Therefore, the area of the opening of the trough is reduced by the cover, which obstructs the collection of the chips and the machining fluid in the trough.
According to the second prior art, the area of the trough opening is increased, because the two screws for feeding the table are disposed at the outside of the trough. However, in the second prior art, the number of the feed screws is increase by one, and a mechanism and a controller for driving the two feed screws in synchronization with each other are required. Therefore, there are problems that the configuration becomes complex and the production cost is increased.
The provision of the mechanical chip conveyer in the trough results in the problems of the complex configuration and increase in the production cost. In case that the fluid chip conveyer is employed, in addition to the machining fluid pump for supplying the machining fluid to the process nozzle, a machining fluid pump is required for supplying the machining fluid to the chip conveyer nozzle.